Separator, method for preparing same, and electrochemical device and electronic device comprising same

Abstract

The invention discloses a diaphragm and a preparation method thereof, and an electrochemical device and an electronic device comprising the diaphragm, the diaphragm comprises a porous base material and a porous coating arranged on at least one side of the porous base material, the porous coating comprises first filler particles, second microsphere particles and a binder, the first filler particles are of a solid structure, and the second microsphere particles are of a solid structure. Each second microsphere particle comprises a cavity and a shell wrapping the cavity, and the average thickness of the shell ranges from 0.05 micrometer to 0.2 micrometer. The electrochemical device has both good cycle performance and thermal safety performance.

Description

[0001] This application is a divisional application based on the invention with application number 202510059761.2, application date January 15, 2025, applicant Ningde New Energy Technology Co., Ltd., and invention name “Diaphragm, and electrochemical device and electronic device containing the same”. Technical Field

[0002] The present application belongs to the field of electrochemical technology, and specifically relates to a diaphragm and a preparation method thereof, as well as an electrochemical device and an electronic device containing the same. Background Art

[0003] As the demand for high energy density of lithium-ion batteries continues to increase, the compaction density of electrode plates continues to increase, and the thickness of the diaphragm continues to decrease, resulting in a reduction in the internal electrolyte storage space of the lithium-ion battery and a reduction in the electrolyte retention volume. During the use of lithium-ion batteries, as the cycle of charge and discharge progresses, the electrolyte retention volume gradually decreases, and purple spots and lithium precipitation are prone to appear at the interface of the electrode plates, and even lead to cycle diving. If the problem of reduced electrolyte retention volume is improved by increasing the electrolyte injection volume, lithium-ion batteries, especially soft-pack lithium-ion batteries, are prone to liquid swelling after packaging, which will also affect the use of lithium-ion batteries. Summary of the Invention

[0004] The present application provides a diaphragm and a preparation method thereof, as well as an electrochemical device and an electronic device comprising the same. The electrochemical device has both good cycle performance and thermal safety performance.

[0005] In the first aspect, the present application provides a diaphragm comprising a porous substrate and a porous coating arranged on at least one side of the porous substrate, the porous coating comprising first filler particles, second microsphere particles and a binder, the first filler particles being a solid structure, the second microsphere particles comprising a cavity and a shell covering the cavity, and the average thickness of the shell being 0.05 μm to 0.2 μm.

[0006] The diaphragm provided in the embodiments of the present application has high heat resistance, good electrolyte wettability and good electrolyte liquid retention. When used in electrochemical devices, it can improve the problem of liquid swelling and the problem of purple spots and lithium precipitation on the interface, thereby enabling the electrochemical device to have both good cycle performance and thermal safety performance.

[0007] In some embodiments, the average thickness of the shell is 0.05 μm to 0.1 μm. A shell within this range is more conducive to improving the problem of liquid swelling and purple spot lithium precipitation at the interface, and is more conducive to improving the cycle performance of the electrochemical device.

[0008] In some embodiments, the average particle size of the first filler particles is 0.2 μm to 2 μm, and optionally 0.6 μm to 1 μm. This can result in a higher energy density for the electrochemical device and a higher packing density for the porous coating, thereby improving the heat resistance of the separator and the thermal safety performance of the electrochemical device. Furthermore, the porous coating can have more pores, thereby improving the ion transport properties of the separator and the cycling performance of the electrochemical device.

[0009] In some embodiments, the average particle size of the second microsphere particles is 0.2 μm to 1 μm, and optionally 0.6 μm to 1 μm. This can result in a higher energy density for the electrochemical device and a higher packing density for the porous coating, thereby improving the heat resistance of the separator and the thermal safety performance of the electrochemical device. Furthermore, the porous coating can have more pores, thereby improving the ion transport properties of the separator and the cycling performance of the electrochemical device.

[0010] In some embodiments, the diameter of the cavity of the second microsphere particles is 0.1 μm to 0.9 μm, and optionally 0.4 μm to 0.8 μm. This makes the second microsphere particles easier to process and coat on the separator, while also providing more electrolyte storage space, improving electrolyte swelling and interfacial purple spot lithium precipitation issues, and enhancing the cycling performance of the electrochemical device.

[0011] In some embodiments, the ratio of the diameter of the second microsphere cavity to the average particle size of the second microsphere is 0.6:1 to 0.9:1, and optionally 0.6:1 to 0.88:1. This makes the second microsphere easy to process and coat on the separator, while also providing more electrolyte storage space, improving electrolyte swelling and interfacial purple spot lithium precipitation issues, and enhancing the cycling performance of the electrochemical device.

[0012] In some embodiments, the specific surface area of ​​the second microsphere particles is 5 m 2 / g to 30m 2 The second microsphere particles meeting this specific surface area range have a suitable area for contact with the electrolyte, thereby improving the wettability of the electrolyte, alleviating the problem of electrolyte swelling and the problem of purple spot lithium precipitation at the interface, and improving the cycle performance of the electrochemical device.

[0013] In some embodiments, the shell includes a plurality of pore structures, and the average pore size of the pore structures of the shell is less than 20 nm. When the average pore size of the pore structure of the shell of the second microsphere particle meets the range of this application, the liquid retention capacity and liquid storage effect of the second microsphere particle can be within a suitable range, thereby further improving the cycling performance of the electrochemical device.

[0014] In some embodiments, the average particle size of the first filler particles is greater than or equal to the average particle size of the second microsphere particles. By ensuring that the average particle size of the first filler particles is greater than or equal to the average particle size of the second microsphere particles, the hollow structure of the second microsphere particles can be better maintained, and the risk of deformation of the second microsphere particles due to expansion and compression of the electrode sheet during the charge and discharge cycle of the electrochemical device can be reduced. This can ensure that the second microsphere particles have good liquid retention and storage capabilities, thereby further helping to further improve the cycling performance of the electrochemical device.

[0015] In some embodiments, the first filler particles account for 73% to 94% by mass of the porous coating, the second microsphere particles account for 2% to 20% by mass of the porous coating, and the binder accounts for 1% to 7% by mass of the porous coating. By ensuring that the mass ratios of the first filler particles and the second microsphere particles are within the above ranges, the separator can have high heat resistance, good electrolyte wettability, and good electrolyte retention, thereby improving the problem of electrolyte swelling and interfacial purple spot lithium precipitation, and helping the electrochemical device achieve both good thermal safety and good cycling performance.

[0016] Optionally, the first filler particles account for 80% to 91% by weight of the porous coating, the second microsphere particles account for 5% to 16% by weight of the porous coating, and the binder accounts for 1% to 5% by weight of the porous coating. Meeting this mass ratio of the first filler particles and the second microsphere particles is more conducive to the electrochemical device having both good thermal safety and good cycling performance.

[0017] In some embodiments, the ionic resistance of the porous coating of the separator is 0.001Ω to 0.15Ω. The low ionic resistance of the porous coating of the separator has good ion transport capacity and kinetic performance, which is beneficial to improving the cycling performance of the electrochemical device.

[0018] In some embodiments, the difference between the air permeability of the membrane and the air permeability of the porous substrate is greater than 0 and less than or equal to 20 s / 100 ml. A small difference between the air permeability of the membrane and the air permeability of the porous substrate indicates that the porous coating of the membrane has high air permeability.

[0019] In some embodiments, the shell thickness of the second microsphere particles increases by less than or equal to 80% after being immersed in an electrolyte at 60°C for 24 hours. The second microsphere particles have a low degree of swelling in the electrolyte and high structural stability, thereby improving the electrolyte swelling problem and the problem of purple spot lithium precipitation at the interface, and enhancing the cycling performance of the electrochemical device.

[0020] In some embodiments, the shell of the second microsphere particle includes a first shell layer and a second shell layer, the second shell layer being located between the first shell layer and the second microsphere particle's cavity, the first shell layer comprising polystyrene, and the second shell layer comprising an acrylic polymer, the first shell layer and the second shell layer being connected by a C-C covalent bond. The first shell layer comprising polystyrene can impart high mechanical strength and excellent resistance to electrolyte swelling to the second microsphere particle, while the second shell layer comprising an acrylic polymer can easily form a porous structure, thereby reducing the ionic impedance of the separator, improving the problem of liquid swelling and interfacial purple spot lithium precipitation, and enhancing the cycling performance of the electrochemical device.

[0021] In some embodiments, the acrylic polymer includes soft monomer structural units and hard monomer structural units, the soft monomer structural units include at least one of n-butyl acrylate structural units, n-pentyl acrylate structural units, isopentyl acrylate structural units, isooctyl acrylate structural units, 2-ethylhexyl acrylate structural units, 2-nonyl acrylate structural units, isononyl acrylate structural units, decyl acrylate structural units, undecyl acrylate structural units, lauryl acrylate structural units, tridecyl acrylate structural units, octadecyl acrylate structural units, decyl methacrylate structural units, undecyl methacrylate structural units, lauryl methacrylate structural units, tridecyl methacrylate structural units, and octadecyl methacrylate structural units, and the hard monomer structural units include at least one of methyl acrylate structural units, methyl methacrylate structural units, vinyl acetate structural units, acrylonitrile structural units, acrylamide structural units, and styrene structural units.

[0022] In some embodiments, the mass ratio of the soft monomeric structural units to the hard monomeric structural units is 40:60 to 20:80.

[0023] In some embodiments, the acrylic polymer further comprises a multifunctional cross-linking structural unit, and the multifunctional cross-linking structural unit comprises at least one of an ethylene glycol dimethacrylate structural unit, a polyethylene glycol dimethacrylate structural unit, a butylene glycol dimethacrylate structural unit, a hexanediol dimethacrylate structural unit, a polybutadiene dimethacrylate structural unit, a polyurethane dimethacrylate structural unit, a propoxylated glycerol trimethacrylate structural unit, and a divinylbenzene structural unit.

[0024] In some embodiments, the mass of the multifunctional cross-linking structural unit is 0.1% to 10% of the total mass of the soft monomer structural unit and the hard monomer structural unit.

[0025] In some embodiments, the acrylic polymer is composed of n-butyl acrylate structural units, methyl acrylate structural units, and ethylene glycol dimethacrylate structural units. In the acrylic polymer, the mass ratio of the n-butyl acrylate structural units to the methyl acrylate structural units is 40:60 to 20:80, and the mass of the ethylene glycol dimethacrylate structural units is 0.5% to 10% of the total mass of the n-butyl acrylate structural units and the methyl acrylate structural units.

[0026] In some embodiments, the specific surface area of ​​the first filler particles is less than or equal to 20 m 2 This helps to improve the heat resistance of the separator and the thermal safety performance of the electrochemical device.

[0027] In some embodiments, the glass transition temperature of the binder is g -40℃ to 15℃.

[0028] In some embodiments, the binder includes at least one of polymethacrylate binders, styrene-butadiene rubber, polyacrylic acid, and polyacrylate.

[0029] In some embodiments, the porous substrate has a thickness of 2 μm to 7 μm. A porous substrate having such a thickness is more conducive to improving the energy density of the electrochemical device.

[0030] In some embodiments, the porous coating has a thickness of 0.5 μm to 3 μm, which is more conducive to the electrochemical device having high energy density, good cycle performance and thermal safety performance.

[0031] In some embodiments, the total thickness of the separator is 2.5 μm to 10 μm.

[0032] In some embodiments, the bonding force between the porous substrate and the porous coating is 30 N / m to 100 N / m. High bonding force between the porous substrate and the porous coating improves the stability of the separator, and the porous coating is less likely to shed, which is more conducive to good cycling performance of the electrochemical device.

[0033] In some embodiments, the longitudinal thermal shrinkage of the separator after heating at 130° C. for 1 hour is less than or equal to 5%.

[0034] In some embodiments, the transverse thermal shrinkage of the separator when heated at 130° C. for 1 hour is less than or equal to 5%.

[0035] The diaphragm has a small thermal shrinkage rate and good heat resistance, which is more conducive to the electrochemical device having good thermal safety performance.

[0036] In a second aspect, the present application provides an electrochemical device comprising a positive electrode sheet, a negative electrode sheet, and the diaphragm of the first aspect of the present application, wherein the diaphragm is located between the positive electrode sheet and the negative electrode sheet.

[0037] In a third aspect, the present application provides an electronic device comprising the electrochemical device according to the second aspect of the present application.

[0038] In a fourth aspect, the present application provides a method for preparing a diaphragm, comprising the following steps: providing a porous substrate; providing a porous coating slurry comprising first filler particles, second microsphere particles and a binder, wherein the first filler particles are a solid structure, the second microsphere particles comprise a cavity and a shell covering the cavity, and the average thickness of the shell is 0.05 μm to 0.2 μm; coating the porous coating slurry on at least one side of the porous substrate, and obtaining a diaphragm after drying. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The relevant embodiments described herein are illustrative and are used to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as limiting the present application. Based on the technical solutions and embodiments provided in the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present application.

[0040] For the sake of clarity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0041] In the description herein, unless otherwise specified, “above” and “below” include the number itself.

[0042] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application). Unless otherwise specified, the test temperature of each parameter mentioned in this application is 25°C and the test pressure is standard atmospheric pressure.

[0043] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0044] The term "plurality" means more than two.

[0045] The diaphragm is an important component of the electrochemical device. It separates the positive and negative electrodes and prevents contact short circuits in the electrochemical device. The diaphragm can also close its pores at a certain temperature, blocking the transmission of lithium ions and the flow of current, preventing direct contact and short circuits between the positive and negative electrodes, thereby reducing problems such as combustion and explosion in the electrochemical device. At the same time, the diaphragm also needs to be able to absorb and retain a certain amount of electrolyte in its pore structure, forming an ion transmission channel, realizing lithium ion migration, and completing the electrochemical charge and discharge process.

[0046] As the thickness of the diaphragm continues to decrease, the electrolyte storage space it can provide decreases, and the electrolyte's liquid retention capacity becomes worse. During the use of the electrochemical device, purple spots and lithium deposition are prone to occur at the electrode plate interface, and even cause the electrochemical device to experience cycle diving.

[0047] Currently, separators typically include a porous substrate and a ceramic coating disposed on at least one side of the porous substrate. Increasing the porosity of the porous substrate can improve the separator's electrolyte retention. However, as the porosity of the porous substrate continues to increase, its structural strength deteriorates, the separator's heat resistance deteriorates, and the separator's closed-cell properties deteriorate, making it unable to block the transmission of lithium ions and the flow of current when the electrochemical device overheats. This can cause direct contact and short circuits between the positive and negative electrodes, which is detrimental to improving the thermal safety of the electrochemical device. Increasing the electrolyte injection volume can easily lead to electrolyte swelling after the electrochemical device is packaged, which can also affect the use of the electrochemical device.

[0048] Based on this, from the perspective of the diaphragm, the present application adjusts the composition of the porous coating of the diaphragm to enable the diaphragm to have high heat resistance, good electrolyte wettability and good electrolyte retention. When used in electrochemical devices, it can improve the problem of liquid swelling and the problem of purple spot lithium precipitation at the interface caused by electrolyte shortage, thereby enabling the electrochemical device to have both good cycle performance and thermal safety performance.

[0049] In a first aspect, an embodiment of the present application provides a diaphragm.

[0050] The separator provided in the embodiments of the present application includes a porous substrate and a porous coating disposed on at least one side of the porous substrate. The porous coating includes first filler particles, second microsphere particles, and a binder. The second microsphere particles include a cavity and a shell encapsulating the cavity. The shell includes multiple pores and has an average thickness of 0.05 μm to 0.2 μm. The first filler particles in the present application do not have a hollow structure.

[0051] The porous coating of the diaphragm of the present application includes second microsphere particles, which are hollow structures and have a shell including multiple pore structures. The pore structure connects the outside and the cavity, which can increase the porosity of the porous coating, so that the porous coating and the diaphragm have lower ionic impedance; in addition, after injection, the electrolyte can enter the cavity through the pore structure of the shell, thereby increasing the electrolyte storage space of the porous coating, allowing more electrolyte to be stored in the diaphragm, and improving the liquid swelling problem; in addition, during the cyclic charge and discharge process of the electrochemical device, especially in the later stage of the cycle, the electrolyte stored in the cavity can also be released through the pore structure of the shell, thereby reducing the problem of interfacial purple spot lithium precipitation caused by electrolyte shortage and improving the cycle performance of the electrochemical device using the diaphragm.

[0052] The greater the thickness of the shell of the second microsphere particle, the smaller the electrolyte storage space that can be provided, and the smaller the improvement effect on the liquid swelling problem and the interface purple spot lithium precipitation problem; at the same time, the thickness of the shell of the second microsphere particle should not be too small. On the one hand, the difficulty of preparing the second microsphere particle increases and the production cost increases. On the other hand, the structural strength and processing performance of the second microsphere particle deteriorate. The risk of shell deformation and rupture increases during the diaphragm preparation process, the electrochemical device assembly process, and the electrochemical device cyclic charge and discharge process. After the shell is deformed, the liquid retention capacity and liquid storage effect of the second microsphere particle deteriorate or even lose. After the shell is ruptured, the ionic impedance of the porous coating and the diaphragm is increased. The present application makes the average thickness of the shell from 0.05 μm to 0.2 μm, which can make the second microsphere particle easy to process and easy to coat on the diaphragm, and can provide more electrolyte storage space, improve the liquid swelling problem and the interface purple spot lithium precipitation problem.

[0053] The porous coating layer of the separator of the present application further includes first filler particles, which can improve the heat resistance of the separator.

[0054] Therefore, the diaphragm provided in the embodiment of the present application has high heat resistance, good electrolyte wettability and good electrolyte liquid retention. When used in an electrochemical device, it can improve the problem of liquid swelling and the problem of purple spots and lithium precipitation at the interface, thereby enabling the electrochemical device to have both good cycle performance and thermal safety performance.

[0055] The average thickness of the shell is 0.05μm to 0.2μm, for example, it can be 0.05μm, 0.055μm, 0.06μm, 0.065μm, 0.07μm, 0.075μm, 0.08μm, 0.085μm, 0.09μm, 0.095μm, 0.1μm, 0.11μm, 0.12μm, 0.13μm, 0.14μm, 0.15μm, 0.16μm, 0.17μm, 0.18μm, 0.19μm, 0.2μm, or a range consisting of any of the above values.

[0056] Optionally, the average thickness of the shell can be 0.05μm to 0.18μm, 0.05μm to 0.15μm, 0.05μm to 0.12μm, 0.05μm to 0.1μm, 0.06μm to 0.18μm, 0.06μm to 0.15μm, 0.06μm to 0.12μm, 0.06μm to 0.1μm, 0.07μm to 0.18μm, 0.07μm to 0.15μm, 0.07μm to 0.12μm, 0.07μm to 0.1μm, 0.08μm to 0.18μm, 0.08μm to 0.15μm, 0.08μm to 0.12μm, 0.08μm to 0.1μm.

[0057] A shell that meets this range is more conducive to improving the liquid swelling problem and the purple spot lithium precipitation problem on the interface, and is more conducive to improving the cycle performance of the electrochemical device.

[0058] In some embodiments, the mass proportion of the first filler particles in the porous coating layer can be 73% to 94%, for example, it can be 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, or a range consisting of any of the above values.

[0059] In some embodiments, the mass proportion of the second microsphere particles in the porous coating layer can be 2% to 20%, for example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range consisting of any of the above values.

[0060] By ensuring that the mass ratio of the first filler particles to the second microsphere particles is within the above range, the first filler particles can be fully utilized for their high heat resistance, and the hollow structure of the second microsphere particles can be maintained, thereby better utilizing the second microsphere particles to store and retain the electrolyte. Therefore, by ensuring that the mass ratio of the first filler particles to the second microsphere particles is within the above range, the separator can have high heat resistance, good electrolyte wettability, and good electrolyte retention, thereby improving the problem of electrolyte swelling and interfacial purple spot lithium precipitation, and helping the electrochemical device to have both good thermal safety performance and good cycle performance.

[0061] Optionally, the mass proportion of the first filler particles in the porous coating layer may be 80% to 91%.

[0062] Optionally, the mass proportion of the second microsphere particles in the porous coating layer may be 5% to 16%.

[0063] The first filler particles and the second microsphere particles meeting this mass ratio are more conducive to the electrochemical device having both good thermal safety performance and good cycle performance.

[0064] In some embodiments, the binder may account for 1% to 7% by weight of the porous coating, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or any range thereof.

[0065] The binder is used to bond the first filler particles and the second microsphere particles to the porous substrate. By ensuring that the mass ratio of the binder in the porous coating is within the above range, the first filler particles and the second microsphere particles can be firmly bonded to the porous substrate, reducing the problem of powder loss.

[0066] Optionally, the binder may account for 1% to 5% by mass in the porous coating layer.

[0067] In some embodiments, the first filler particles may be solid, which helps to improve the heat resistance of the separator and the thermal safety performance of the electrochemical device.

[0068] In the present application, the first filler particles being a solid structure does not mean that the first filler particles are absolutely non-porous. The first filler particles may also be a nearly solid structure.

[0069] In some embodiments, the specific surface area of ​​the first filler particles may be less than or equal to 20 m 2 This helps to improve the heat resistance of the separator and the thermal safety performance of the electrochemical device.

[0070] Optionally, the specific surface area of ​​the first filler particles may be less than or equal to 15 m 2 / g, less than or equal to 10m 2 / g.

[0071] In some embodiments, the average particle size of the first filler particles can be 0.2 μm to 2 μm, for example, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, or a range consisting of any of the above values.

[0072] If the average particle size of the first filler particles is too large (for example, greater than 2 μm), it is difficult to achieve a thin coating design of the porous coating, thereby affecting the energy density of the electrochemical device; if the average particle size of the first filler particles is too small (for example, less than 0.2 μm), it is easy to cause the first filler particles to accumulate and reduce the pore size, affecting ion transport, thereby affecting the cycle performance of the electrochemical device. By making the average particle size of the first filler particles 0.2 μm to 2 μm, the electrochemical device can have a higher energy density, the porous coating can have a higher packing density, thereby improving the heat resistance of the diaphragm and the thermal safety performance of the electrochemical device, and the porous coating can have more pores, thereby improving the ion transport characteristics of the diaphragm and the cycle performance of the electrochemical device.

[0073] Optionally, the average particle size of the first filler particles may be 0.3 μm to 1.8 μm, 0.3 μm to 1.6 μm, 0.3 μm to 1.4 μm, 0.3 μm to 1.2 μm, 0.3 μm to 1 μm, 0.4 μm to 1.8 μm, 0.4 μm to 1.6 μm, 0.4 μm to 1.4 μm, 0.4 μm to 1.2 μm, 0.4 μm to 1 μm, 0.5 μm to 1.8 μm, 0.5 μm to 1.6 μm, 0.5 μm to 1.4 μm, 0.5 μm to 1.2 μm, 0.5 μm to 1 μm, 0.6 μm to 1.8 μm, 0.6 μm to 1.6 μm, 0.6 μm to 1.4 μm, 0.6 μm to 1.2 μm, 0.6 μm to 1 μm.

[0074] The first filler particles meeting this range are more conducive to improving the thermal safety and cycle performance of the electrochemical device.

[0075] In some embodiments, the first filler particles may include at least one of inorganic particles and organic particles. Alternatively, the first filler particles may include inorganic particles.

[0076] In some embodiments, the inorganic particles may include ceramic particles. By way of example, the ceramic particles may include, but are not limited to, at least one of boehmite, aluminum oxide, zirconium oxide, titanium dioxide, magnesium oxide, silicon oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, yttrium oxide, mullite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium sulfate, silicon carbide, silicon nitride, boron nitride, and aluminum nitride.

[0077] In some embodiments, the organic particles may include at least one of melamine and dicyandiamide.

[0078] In some embodiments, the average particle size of the second microsphere particles may be 0.2 μm to 1 μm, for example, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, or any range thereof.

[0079] The average particle size of the second microsphere particles is too small (for example, less than 0.2 μm), which easily leads to a decrease in the pores of the second microsphere particles, affecting ion transmission, thereby affecting the cycle performance of the electrochemical device. At the same time, the preparation difficulty of the second microsphere particles increases and the production cost increases. By making the average particle size of the second microsphere particles 0.2 μm to 1 μm, the electrochemical device can have a higher energy density, the porous coating can have a higher packing density, thereby improving the heat resistance of the diaphragm and the thermal safety performance of the electrochemical device. The porous coating can also have more pores, thereby improving the ion transmission characteristics of the diaphragm and improving the cycle performance of the electrochemical device.

[0080] Optionally, the average particle size of the second microsphere particles may be 0.3 μm to 1 μm, 0.4 μm to 1 μm, 0.5 μm to 1 μm, or 0.6 μm to 1 μm.

[0081] The second microsphere particles meeting this range are more conducive to improving the cycle performance of the electrochemical device.

[0082] In some embodiments, the diameter of the cavity of the second microsphere particle can be 0.1 μm to 0.9 μm, for example, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm, 0.9 μm, or a range consisting of any of the above values.

[0083] The diameter of the cavity of the second microsphere particle is small, and the electrolyte storage space that can be provided is small, and the improvement effect on the liquid swelling problem and the problem of purple spot lithium precipitation at the interface is small; at the same time, the diameter of the cavity of the second microsphere particle should not be too large. At this time, the structural strength and processing performance of the second microsphere particle deteriorate, and the risk of shell deformation and rupture increases during the diaphragm preparation process, the electrochemical device assembly process, and the electrochemical device cyclic charge and discharge process. The present application makes the diameter of the cavity of the second microsphere particle 0.1μm to 0.9μm, which can make the second microsphere particle easy to process and easy to coat on the diaphragm, and can provide more electrolyte storage space, improve the problem of liquid swelling and the problem of purple spot lithium precipitation at the interface, and improve the cycle performance of the electrochemical device.

[0084] Optionally, the diameter of the cavity of the second microsphere particle may be 0.2 μm to 0.9 μm, 0.3 μm to 0.9 μm, 0.4 μm to 0.9 μm, 0.2 μm to 0.85 μm, 0.3 μm to 0.85 μm, 0.4 μm to 0.85 μm, 0.2 μm to 0.8 μm, 0.3 μm to 0.8 μm, 0.4 μm to 0.8 μm.

[0085] The second microsphere particles meeting this range are more conducive to improving the cycle performance of the electrochemical device.

[0086] In some embodiments, the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle can be 0.6:1 to 0.9:1, for example, 0.6:1, 0.62:1, 0.64:1, 0.66:1, 0.68:1, 0.7:1, 0.72:1, 0.74:1, 0.76:1, 0.78:1, 0.8:1, 0.82:1, 0.84:1, 0.86:1, 0.88:1, 0.9:1, or a range consisting of any of the above values.

[0087] The ratio of the diameter of the cavity of the second microsphere particles to the average particle size of the second microsphere particles is small, and the electrolyte storage space that can be provided is small, and the improvement effect on the liquid swelling problem and the interface purple spot lithium precipitation problem is small; at the same time, the ratio of the diameter of the cavity of the second microsphere particles to the average particle size of the second microsphere particles should not be too large. On the one hand, the difficulty of preparing the second microsphere particles increases and the production cost increases. On the other hand, the structural strength and processing performance of the second microsphere particles deteriorate, and the risk of shell deformation and rupture increases during the diaphragm preparation process, the electrochemical device assembly process, and the electrochemical device cyclic charge and discharge process. The present application makes the ratio of the diameter of the cavity of the second microsphere particles to the average particle size of the second microsphere particles from 0.6:1 to 0.9:1, which can not only make the second microsphere particles easy to process and easy to coat on the diaphragm, but also provide more electrolyte storage space, improve the liquid swelling problem and the interface purple spot lithium precipitation problem, and improve the cycle performance of the electrochemical device.

[0088] Alternatively, the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle can be 0.6:1 to 0.9:1, 0.62:1 to 0.9:1, 0.64:1 to 0.9:1, 0.66:1 to 0.9:1, 0.6:1 to 0.88:1, 0.62:1 to 0.88:1, 0.64:1 to 0.88:1, 0.66:1 to 0.88:1, 0.6:1 to 0.84:1, 0.62:1 to 0.84:1, 0.64:1 to 0.84:1, 0.66:1 to 0.84:1, 0.6:1 to 0.8:1, 0.62:1 to 0.8:1, 0.64:1 to 0.8:1, 0.66:1 to 0.8:1.

[0089] The second microsphere particles meeting this range are more conducive to improving the cycle performance of the electrochemical device.

[0090] In some embodiments, the specific surface area of ​​the second microsphere particles can be 5m 2 / g to 30m 2 / g, for example, 5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g、10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g、15m 2 / g、16m 2 / g、17m 2 / g、18m 2 / g、19m 2 / g, 20m 2 / g, 21m 2 / g、22m 2 / g, 23m 2 / g、24m 2 / g, 25m 2 / g、26m 2 / g、27m 2 / g、28m 2 / g、29m 2 / g、30m 2 / g, or any range consisting of the above values.

[0091] The second microsphere particles meeting this specific surface area range have a suitable area for contact with the electrolyte, thereby improving the wettability of the electrolyte, helping to alleviate the problem of liquid swelling and interface purple spot lithium precipitation, and helping to improve the cycle performance of the electrochemical device.

[0092] In some embodiments, the average pore size of the pore structure of the shell of the second microsphere particle can be less than 20 nm.

[0093] When the average pore size of the pore structure of the shell of the second microsphere particle meets the range of this application, the liquid retention capacity and liquid storage effect of the second microsphere particle can be kept within an appropriate range, thereby further improving the cycling performance of the electrochemical device. When the average pore size is too large, the liquid retention capacity and liquid storage effect of the second microsphere particle deteriorate, which is not conducive to better improving the liquid swelling problem and the problem of purple spot lithium precipitation at the interface, nor is it conducive to further improving the cycling performance of the electrochemical device.

[0094] In some embodiments, the thickness increase rate of the shell of the second microsphere particles after being immersed in the electrolyte at 60° C. for 24 hours may be less than or equal to 80%.

[0095] The second microsphere particles have a small degree of swelling in the electrolyte and a high structural stability, which is beneficial to improving the problem of liquid swelling and the problem of purple spots and lithium precipitation at the interface, as well as improving the cycle performance of the electrochemical device.

[0096] The thickness growth rate of the shell of the second microsphere particle after being immersed in the electrolyte at 60°C for 24 hours can be tested according to the following method: disassemble the electrochemical device, take out a certain amount of free electrolyte, dry the diaphragm and test the average thickness of the shell of the second microsphere particle, recorded as H1, then soak the dried diaphragm in the electrolyte at 60°C, take it out after 24 hours, and test the average thickness of the shell of the second microsphere particle again, recorded as H2, and (H2-H1) / H1*100% represents the thickness growth rate of the shell of the second microsphere particle after being immersed in the electrolyte at 60°C for 24 hours.

[0097] In some embodiments, the shell of the second microsphere particle may include a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity of the second microsphere particle, the first shell layer may include polystyrene, the second shell layer may include an acrylic polymer, and the first shell layer and the second shell layer are connected by a CC covalent bond.

[0098] The first shell layer includes polystyrene, which can make the second microsphere particles have higher mechanical strength and better resistance to electrolyte swelling; the second shell layer includes acrylic polymer, which can easily form a porous structure, thereby reducing the ionic impedance of the diaphragm, improving the liquid swelling problem and the interface purple spot lithium precipitation problem, and improving the cycle performance of the electrochemical device.

[0099] The second shell layer includes an acrylic polymer. In some embodiments, the acrylic polymer may include soft monomer structural units and hard monomer structural units.

[0100] Optionally, the soft monomer structural unit may include at least one of n-butyl acrylate structural unit, n-pentyl acrylate structural unit, isopentyl acrylate structural unit, isooctyl acrylate structural unit, 2-ethylhexyl acrylate structural unit, 2-nonyl acrylate structural unit, isononyl acrylate structural unit, decyl acrylate structural unit, undecyl acrylate structural unit, lauryl acrylate structural unit, tridecyl acrylate structural unit, octadecyl acrylate structural unit, decyl methacrylate structural unit, undecyl methacrylate structural unit, lauryl methacrylate structural unit, tridecyl methacrylate structural unit, and octadecyl methacrylate structural unit.

[0101] Optionally, the hard monomer structural unit may include at least one of a methyl acrylate structural unit, a methyl methacrylate structural unit, a vinyl acetate structural unit, an acrylonitrile structural unit, an acrylamide structural unit, and a styrene structural unit.

[0102] Optionally, the mass ratio of the soft monomer structural unit to the hard monomer structural unit can be 40:60 to 20:80, for example, it can be 40:60, 39:61, 38:62, 37:63, 36:64, 35:65, 34:66, 33:67, 32:68, 31:69, 30:70, 29:71, 28:72, 27:73, 26:74, 25:75, 24:76, 23:77, 22:78, 21:79, 20:80, or a range consisting of any of the above values.

[0103] Adjusting the mass ratio of the soft monomer structural unit to the hard monomer structural unit can make the second shell have both high mechanical strength and good resistance to electrolyte swelling, which is beneficial for the porous coating and the separator to have low ionic resistance.

[0104] In some embodiments, the acrylic polymer may further include multifunctional cross-linking structural units.

[0105] By making the acrylic polymer further include multifunctional cross-linked structural units, the mechanical strength and electrolyte swelling resistance of the second shell can be improved, thereby improving the structural stability of the second microsphere particles and also facilitating the porous coating and the separator to have lower ionic resistance.

[0106] Optionally, the multifunctional cross-linking structural unit may include at least one of an ethylene glycol dimethacrylate structural unit, a polyethylene glycol dimethacrylate structural unit, a butylene glycol dimethacrylate structural unit, a hexanediol dimethacrylate structural unit, a polybutadiene dimethacrylate structural unit, a polyurethane dimethacrylate structural unit, a propoxylated glycerol trimethacrylate structural unit, and a divinylbenzene structural unit.

[0107] Optionally, the mass of the multifunctional cross-linked structural unit can be 0.1% to 10% of the total mass of the soft monomer structural unit and the hard monomer structural unit, for example, it can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any of the above values.

[0108] In some embodiments, the acrylic polymer may further include functional monomer structural units.

[0109] Optionally, the functional monomer structural unit may include at least one of an acrylic acid structural unit, a methacrylic acid structural unit, an itaconic acid structural unit, a hydroxyethyl acrylate structural unit, a hydroxypropyl acrylate structural unit, a hydroxybutyl acrylate structural unit, and a glycidyl acrylate structural unit.

[0110] By making the acrylic ester polymer further include a functional monomer structural unit, the functional monomer structural unit contains a lyophilic group, thereby improving the electrolyte wettability of the second shell layer and reducing the ionic resistance of the separator.

[0111] Optionally, the mass of the functional monomer structural unit can be 1% to 20% of the total mass of the soft monomer structural unit and the hard monomer structural unit, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range consisting of any of the above values.

[0112] In some embodiments, the acrylic polymer can be composed of n-butyl acrylate structural units, methyl acrylate structural units, and ethylene glycol dimethacrylate structural units. In the acrylic polymer, the mass ratio of the n-butyl acrylate structural units to the methyl acrylate structural units can be 40:60 to 20:80, and the mass of the ethylene glycol dimethacrylate structural units can be 0.5% to 10% of the total mass of the n-butyl acrylate structural units and the methyl acrylate structural units.

[0113] In some embodiments, the preparation method of the second microsphere particles may include the following steps:

[0114] Through seed polymerization, a "nano seed" is obtained as a core, and the core includes an acrylic polymer;

[0115] Through interfacial polymerization, a coating layer is polymerized on the surface of the "nanoseed" to obtain latex particles with a core-shell structure, wherein the coating layer includes polystyrene;

[0116] The prepared core-shell structured emulsion particles are transferred to an acidic solution, an alkaline solution or an organic solvent, and the solvent penetrates through the coating layer to dissolve the core polymer material. During the dissolution process, the coating layer continuously expands, and the solvent penetrates the coating layer to form a through pore structure. The dissolved polymer material can be discharged through the pore structure to form a cavity of the second microsphere particle. The remaining part (including the undissolved polymer material and the coating layer) serves as the shell of the second microsphere particle. The shell includes multiple pore structures, the shell includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity, the first shell layer includes polystyrene, the second shell layer includes an acrylic polymer, and the first shell and the second shell are connected by a C-C covalent bond.

[0117] In some embodiments, the average particle size of the first filler particles may be greater than or equal to the average particle size of the second microsphere particles.

[0118] By making the average particle size of the first filler particles greater than or equal to the average particle size of the second microsphere particles, the hollow structure of the second microsphere particles can be better maintained, and the risk of deformation of the second microsphere particles due to expansion and extrusion of the electrode sheets during the cyclic charge and discharge process of the electrochemical device can be reduced. This can enable the second microsphere particles to have good liquid retention and storage effects, thereby helping to further improve the cycle performance of the electrochemical device.

[0119] In some embodiments, the glass transition temperature of the binder is g The temperature may be between -40°C and 15°C, for example, -40°C, -35°C, -30°C, -25°C, -20°C, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, or a range consisting of any of the above values.

[0120] In some embodiments, the binder may include, but is not limited to, at least one of polymethacrylate binders, styrene-butadiene rubber, polyacrylic acid, and polyacrylate.

[0121] In some embodiments, the porous coating layer may further include a wetting agent and / or a dispersant. The wetting agent and / or the dispersant may improve the consistency of the porous coating layer, thereby facilitating reduction of the problem of purple plaque lithium deposition at the interface.

[0122] The present application does not particularly limit the type and content of the dispersant and wetting agent, as long as the purpose of the present application can be achieved. Alternatively, the dispersant may include but is not limited to at least one of sodium carboxymethyl cellulose, polyethylene glycol, polyvinyl pyrrolidone, polyvinyl alcohol compounds, and sodium dodecylbenzene sulfonate. Alternatively, the wetting agent may include but is not limited to at least one of dimethyl siloxane, polyoxyethylene alkylphenol ether, polyoxyethylene fatty alcohol ether, polyoxyethylene polyoxypropylene block copolymer, and polyether-modified trimethyl siloxane.

[0123] In some embodiments, the ionic resistance of the porous coating of the separator can be 0.001Ω to 0.15Ω, for example, 0.001Ω, 0.003Ω, 0.005Ω, 0.008Ω, 0.01Ω, 0.02Ω, 0.03Ω, 0.04Ω, 0.05Ω, 0.06Ω, 0.07Ω, 0.08Ω, 0.09Ω, 0.1Ω, 0.11Ω, 0.12Ω, 0.13Ω, 0.14Ω, 0.15Ω, or a range consisting of any of the above values.

[0124] The ionic resistance of the porous coating of the separator = the ionic resistance of the separator - the ionic resistance of the porous substrate.

[0125] The porous coating of the diaphragm has low ionic impedance, good ion transmission capacity and good kinetic performance, which is beneficial to improving the cycle performance of the electrochemical device.

[0126] In some embodiments, the difference between the air permeability of the membrane and the air permeability of the porous substrate may be greater than 0 and less than or equal to 20 s / 100 ml.

[0127] The difference between the air permeability of the membrane and the air permeability of the porous substrate (ie, the air permeability of the membrane minus the air permeability of the porous substrate) is small, indicating that the porous coating of the membrane has high air permeability.

[0128] Optionally, the difference between the air permeability of the diaphragm and the air permeability of the porous substrate may be greater than 0 and less than or equal to 18 s / 100 ml, greater than 0 and less than or equal to 15 s / 100 ml, greater than 0 and less than or equal to 12 s / 100 ml, greater than 0 and less than or equal to 10 s / 100 ml, or greater than 0 and less than or equal to 9 s / 100 ml.

[0129] In some embodiments, the porous substrate may have a thickness of 2 μm to 7 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, or any range thereof. A porous substrate having such a thickness is more conducive to improving the energy density of the electrochemical device.

[0130] In some embodiments, the porous substrate may have a porosity of 20% to 50%, for example, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, or any range thereof. A porosity within this range is more conducive to improving the cycling performance of the electrochemical device.

[0131] The porosity of a porous substrate can be tested using a true density tester. Place a porous substrate sample on the true density tester to determine the true volume of the porous substrate. Use a ruler to measure the length, width, and height of the sample and calculate the apparent volume of the porous substrate. Porosity (%) of a porous substrate = (Apparent volume of porous substrate - True volume of porous substrate) / Apparent volume of porous substrate × 100%.

[0132] The present application does not particularly limit the material of the porous substrate, as long as the purpose of the present application can be achieved. For example, the porous substrate can be a non-woven fabric, film or composite film having a porous structure, and the material of the porous substrate can include at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, polyamide, spandex and aramid. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film can be used.

[0133] The porous coating layer is disposed on at least one side of the porous substrate. For example, the porous coating layer may be disposed on one side of the porous substrate, or the porous coating layer may be disposed on both sides of the porous substrate.

[0134] In some embodiments, the thickness of the porous coating layer can be 0.5 μm to 3 μm, for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or any range thereof. The thickness of the porous coating layer refers to the thickness of the porous coating layer on a single side of the porous substrate.

[0135] It is understood that if the thickness of the porous coating is too low (e.g., less than 0.5 μm), the structural strength and heat resistance of the separator will decrease; if the thickness of the porous coating is too high (e.g., greater than 3 μm), the separator will become thicker as a whole, which is not conducive to improving the energy density of the electrochemical device. By setting the thickness of the porous coating to 0.5 μm to 3 μm, it is more conducive to the electrochemical device to have high energy density, good cycle performance and thermal safety performance.

[0136] In some embodiments, the total thickness of the separator may be 2.5 μm to 10 μm, for example, 2.5 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or a range consisting of any of the above values.

[0137] In some embodiments, the adhesion between the porous substrate and the porous coating layer can be 30 N / m to 100 N / m, for example, 30 N / m, 40 N / m, 50 N / m, 60 N / m, 70 N / m, 80 N / m, 90 N / m, 100 N / m, or a range consisting of any of the above values.

[0138] The adhesion between the porous substrate and the porous coating can be tested by a 180° peeling test according to GB / T 2790-1995, with a peeling speed of 50 mm / min.

[0139] The bonding force between the porous substrate and the porous coating is high, the stability of the separator is good, and the porous coating is not easy to fall off, which is more conducive to the electrochemical device having good cycle performance.

[0140] In some embodiments, the longitudinal thermal shrinkage of the membrane heated at 130° C. for 1 hour may be less than or equal to 5%. Alternatively, the longitudinal thermal shrinkage of the membrane heated at 130° C. for 1 hour may be less than or equal to 4.5%, less than or equal to 4%, less than or equal to 3.5%, or less than or equal to 3%.

[0141] In some embodiments, the transverse thermal shrinkage of the separator heated at 130° C. for 1 hour may be less than or equal to 5%. Alternatively, the transverse thermal shrinkage of the separator heated at 130° C. for 1 hour may be less than or equal to 4.5%, less than or equal to 4%, less than or equal to 3.5%, or less than or equal to 3%.

[0142] The diaphragm has a small thermal shrinkage rate and good heat resistance, which is more conducive to the electrochemical device having good thermal safety performance.

[0143] The preparation method of the diaphragm may include the following steps: providing a porous substrate; providing a porous coating slurry including first filler particles, second microsphere particles and a binder; coating the porous coating slurry on at least one side of the porous substrate, and obtaining the diaphragm after drying.

[0144] Optionally, the solvent in the slurry may include water.

[0145] The average particle size of each of the above-mentioned particles (such as the first filler particles, the second microsphere particles, etc.) can be tested as follows: use a scanning electron microscope with reference to JY / T010-1996 to obtain an SEM image of the diaphragm, arbitrarily select a test sample with a length × width of 50 mm × 100 mm on the diaphragm, randomly select multiple test areas (for example, 5) in the test sample, and read the particle size of each particle to be tested in each test area at a certain magnification (for example, 500 times or more); count the number and particle size values ​​of the particles to be tested in each test area, and take the arithmetic mean of the particle size of all particles to be tested in each test area as the average particle size of the particles to be tested. In order to ensure the accuracy of the test results, multiple test samples (for example, 10) can be taken for the above test, and the average value of each test sample is taken as the final test result. The testing instrument can be ZEISS Sigma300. It should be noted that when the particle to be tested is irregular in shape, the distance between the two farthest points on the particle to be tested is taken as the particle size of the particle to be tested.

[0146] The diameter of the cavity of the second microsphere particle refers to the straight-line distance passing through the center of the hollow cavity and extending to both ends of the hollow cavity, which can be measured by taking an average value at multiple (eg, more than 50) positions in the diaphragm cross-section image.

[0147] The thickness of the shell of the second microsphere particle refers to the distance between the inner surface and the outer surface of the second microsphere particle. The distance between the inner surface and the outer surface of the second microsphere particle can be measured at multiple (for example, more than 50) positions in the diaphragm cross-section image and then the average value is taken.

[0148] The specific surface area of ​​each of the above particles (such as the first filler particles, the second microsphere particles, etc.) can be measured by nitrogen adsorption method using a specific surface area analyzer (such as TristarⅡ3020M) with reference to GB / T19587-2017.

[0149] electrochemical devices

[0150] In a second aspect, embodiments of the present application provide an electrochemical device, including any device in which an electrochemical reaction occurs to convert chemical energy into electrical energy, and specific examples thereof include all types of lithium primary batteries or lithium secondary batteries. In particular, lithium secondary batteries include lithium-ion secondary batteries.

[0151] During the use of electrochemical devices, oxidation and reduction reactions occur in the electrode active materials during charge and discharge. The negative electrode is the electrode where lithium ions are absorbed or lithiated during charge and lithium is released or delithiated during discharge. The positive electrode is the electrode where lithium ions are released or delithiated during charge and lithium is absorbed or lithiated during discharge.

[0152] In some embodiments, the electrochemical device may include a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, and the separator used in the electrochemical device is the separator of the first aspect of the embodiment of the present application. Therefore, the electrochemical device provided by the embodiment of the present application can have good cycle performance.

[0153] The positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly through a winding process or a lamination process.

[0154] The electrochemical device also includes an outer packaging for encapsulating the electrode assembly and electrolyte. In some embodiments, the outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell, or a soft shell, such as a bag-type soft shell. The soft shell can be made of plastic, such as at least one of aluminum-plastic film, polypropylene, polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0155] The electrolyte solution may include an electrolyte salt and a solvent, wherein the electrolyte salt contains lithium ions. The types of the electrolyte salt and the solvent are not particularly limited and can be selected according to needs.

[0156] In some embodiments, the electrolyte salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), and lithium bis(oxalatoborate) (LiBOB). The above electrolyte salts may be used alone or in combination of two or more.

[0157] In some embodiments, the solvent may include at least one of a carbonate compound, a carboxylate compound, an ether compound, and a sulfone compound. As an example, the solvent may include, but is not limited to, ethylene carbonate (EC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate ( At least one of: methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), γ-butyrolactone, sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), diethyl sulfone (ESE), methyl sulfolane, dimethyl sulfoxide, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl ether, diethyl ether, nitromethane, and N,N-dimethylformamide. The above solvents may be used alone or in combination of two or more.

[0158] The electrolyte solution can be prepared according to conventional methods in the art. For example, the electrolyte solution can be obtained by uniformly mixing components such as a solvent and an electrolyte salt. The order of adding the materials is not particularly limited. For example, the electrolyte salt and other components can be added to the solvent and uniformly mixed to obtain the electrolyte solution.

[0159] The components and their contents in the electrolyte can be determined by conventional methods in the art, for example, by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), etc.

[0160] [Positive electrode]

[0161] The material, composition and manufacturing method of the positive electrode sheet may include any technology known in the prior art.

[0162] In some embodiments, the positive electrode sheet may include a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector.

[0163] In some embodiments, the positive electrode current collector may be in the shape of a plate or foil, which is not limited in this embodiment of the present application.

[0164] In some embodiments, the thickness of the positive electrode current collector may be 6 μm to 25 μm.

[0165] In some embodiments, the material of the positive electrode current collector is not particularly limited, and a material with electronic conductivity can be selected. For example, an element or alloy containing at least one of C, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, Al (such as stainless steel, etc.) can be used.

[0166] From the viewpoints of high conductivity, high stability in the electrolyte, and good antioxidant property, a C layer, Al foil, stainless steel foil, etc. are optional. From the viewpoint of further reducing production costs, Al foil is optional. Those skilled in the art can make adjustments according to actual situations.

[0167] The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material can be selected from materials capable of absorbing and releasing lithium.

[0168] The specific type of the positive electrode active material is not particularly limited and can be selected according to requirements. As an example, the positive electrode active material can include, but is not limited to, lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), lithium iron pyrophosphate (Li2FeP2O7), lithium cobalt oxide (LiCoO2), spinel-type lithium manganese oxide (LiMn2O4), spinel-type lithium nickel manganese oxide, layered lithium manganese oxide (LiMnO2), lithium nickel oxide (LiNiO2), lithium niobate (LiNbO2), lithium ferrite (LiFeO2), lithium manganate (LiMgO2), lithium calcium oxide (LiCaO2), lithium copper oxide (LiCuO2), lithium zinc oxide (LiZnO2), lithium molybdate (LiMoO2), lithium tantalate (LiTaO2), lithium tungstate (LiWO2), lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium-rich materials (such as lithium-rich nickel cobalt manganese oxide), manganese dioxide (MnO2), vanadium oxide, sulfur oxide, silicate oxide, and at least one of their respective modified compounds. These materials can be used alone or in combination of two or more.

[0169] Optionally, the positive electrode active material can include at least one of lithium iron phosphate (LiFePO4), lithium cobalt oxide (LiCoO2), lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, spinel-type lithium nickel manganese oxide, and their respective modified compounds.

[0170] As an example, the molecular formula of lithium nickel cobalt aluminum oxide can be LiNi x Co y Al 1-x-y O2, 0 < x < 1, 0 < y < 1, 0 < x + y < 1. For example, it can include, but is not limited to, LiNi 0.8 Co 0.15 Al 0.05 O2.

[0171] As an example, the molecular formula of lithium nickel cobalt manganese oxide can be LiNi x Co y Mn 1-x-y O2, where 0 < x < 1, 0 < y < 1, 0 < x + y < 1. For example, it can include but is not limited to LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, and at least one of them.

[0172] As an example, spinel-type lithium nickel manganate can include but is not limited to LiNi 0.5 Mn 1.5 O4.

[0173] The modified compounds of the above-mentioned cathode active materials can be doping modification, surface coating modification, or simultaneous doping and coating modification of the cathode active materials.

[0174] In some embodiments, the porosity of the cathode active material layer can be 20% to 35%.

[0175] In some embodiments, the thickness of the cathode active material layer can be 15 μm to 150 μm, and the embodiments of the present application do not limit this. The thickness of the cathode active material layer refers to the thickness of the cathode active material layer on one side of the cathode current collector.

[0176] In some embodiments, the cathode active material layer can include a cathode conductive agent. The cathode conductive agent can include conductive carbon powder. As an example, the cathode conductive agent can include but is not limited to at least one of conductive carbon black, acetylene black (AB), Ketjen black (KB), graphite, carbon fiber, carbon tube, graphene, amorphous carbon, hard carbon, soft carbon, glassy carbon, carbon nanofiber, carbon nanotube (CNT). These materials can be used alone or in combination of two or more.

[0177] In some embodiments, the cathode active material layer can include a cathode binder. The cathode binder can include but is not limited to at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and polyvinyl alcohol (PVA).

[0178] The positive electrode sheet can be prepared according to conventional methods in the art. Typically, the positive electrode active material, positive electrode conductive agent, positive electrode binder, etc. are dispersed in a solvent to form a positive electrode slurry. The positive electrode slurry is then coated on the positive electrode current collector. The positive electrode sheet is obtained through processes such as drying and compaction. The solvent can be N-methylpyrrolidone (NMP), but the present application is not limited thereto.

[0179] The coating method can be a coating method known in the art, such as extrusion coating, gravure coating, micro-gravure coating, electrospraying, transfer coating, etc., which is not limited in the embodiments of the present application.

[0180] [Negative electrode]

[0181] The material, composition and manufacturing method of the negative electrode sheet may include any technology known in the prior art.

[0182] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector.

[0183] In some embodiments, the negative electrode current collector may be in the shape of a plate or foil, which is not limited in the embodiments of the present application.

[0184] In some embodiments, the thickness of the negative electrode current collector may be 4 μm to 25 μm.

[0185] In some embodiments, the negative electrode current collector material is not particularly limited, and materials with good electronic conductivity can be selected. For example, a single element or alloy (such as stainless steel) containing at least one of C, Cu, Ni, Fe, V, Nb, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, and Ag can be used. Alternatively, a composite material can be formed by plating a conductive material with a different conductive material, such as Fe plated with Cu.

[0186] From the viewpoint of high conductivity, high stability in electrolyte and good oxidation resistance, Cu foil, Ni foil, stainless steel foil, etc. are optional. From the viewpoint of further reducing production cost, Cu foil and Ni foil are optional. Those skilled in the art can adjust according to actual conditions.

[0187] The negative electrode active material layer includes a negative electrode active material, which may include at least one of a carbon material and a silicon-based material.

[0188] The mass content of the silicon-based material in the negative electrode active material may be 0% to 25%. A mass content of the silicon-based material of 0% indicates that the negative electrode active material does not contain the silicon-based material.

[0189] As an example, the carbon material may include natural graphite, artificial graphite, or a mixture thereof.

[0190] As an example, the silicon-based material may include at least one of elemental silicon, silicon oxide, a silicon-carbon composite material, and a silicon alloy.

[0191] In some embodiments, the porosity of the negative active material layer may be 25% to 45%.

[0192] In some embodiments, the thickness of the negative electrode active material layer may be 30 μm to 150 μm, which is not limited in the present embodiment. The thickness of the negative electrode active material layer refers to the thickness of the negative electrode active material layer located on one side of the negative electrode current collector.

[0193] In some embodiments, the negative electrode active material layer may include a negative electrode conductive agent. The negative electrode conductive agent may include conductive carbon powder. As an example, the negative electrode conductive agent may include, but is not limited to, at least one of conductive carbon black, acetylene black (AB), Ketjen black (KB), graphite, carbon fiber, carbon tube, graphene, amorphous carbon, hard carbon, soft carbon, glassy carbon, carbon nanofiber, and carbon nanotube (CNT). These materials may be used alone or in combination of two or more.

[0194] In some embodiments, the negative electrode active material layer may include a negative electrode binder. The negative electrode binder may include, but is not limited to, at least one of styrene-butadiene rubber (SBR), acrylonitrile copolymers (e.g., LA-type water-based binders, optionally LA132 or LA133), polyacrylic acid (PAA) and its salts, styrene-acrylic resin, polyvinyl alcohol (PVA), and their respective derivatives. Derivatives generally refer to products derived from the replacement of hydrogen atoms or atomic groups in a polymer with other atoms or atomic groups.

[0195] In some embodiments, the negative electrode active material layer may further include a negative electrode dispersant, thereby improving the film-forming quality of the negative electrode active material layer. As an example, the negative electrode dispersant may include, but is not limited to, at least one of sodium carboxymethyl cellulose (CMC) and its derivatives. Derivatives generally refer to products derived from the replacement of hydrogen atoms or atomic groups in a polymer with other atoms or atomic groups (e.g., amino groups).

[0196] The negative electrode sheet can be prepared according to conventional methods in the art. Typically, the negative electrode active material, negative electrode conductive agent, negative electrode binder, and negative electrode dispersant are dispersed in a solvent to form a negative electrode slurry. The negative electrode slurry is then coated onto the negative electrode current collector. The negative electrode sheet is obtained through processes such as drying and compaction. The solvent may include, but is not limited to, at least one of water, ethanol, acetone, butanone, dimethylformamide, N-methylpyrrolidone, diethylformamide, dimethyl sulfoxide, and tetrahydrofuran.

[0197] The coating method can be a coating method known in the art, such as extrusion coating, gravure coating, micro-gravure coating, electrospraying, transfer coating, etc., which is not limited in the embodiments of the present application.

[0198] The negative electrode sheets provided in the embodiments of the present application do not exclude other additional functional layers in addition to the negative electrode active material layer. For example, in some embodiments, the negative electrode sheet may further include a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode active material layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet may further include a protective layer covering the surface of the negative electrode active material layer.

[0199] electronic devices

[0200] In a third aspect, an embodiment of the present application further provides an electronic device, which includes the electrochemical device of the second aspect of the embodiment of the present application.

[0201] The electronic devices provided in the embodiments of the present application are not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic devices can include, but are not limited to, laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors.

[0202] Example

[0203] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing. The instruments used in the examples are commercially available.

[0204] Test section

[0205] (1) Particle size test

[0206] The average particle size of the first filler particles and the second microsphere particles is tested as follows: use a scanning electron microscope with reference to JY / T010-1996 to obtain an SEM image of the diaphragm, arbitrarily select a test sample with a length × width of 50mm × 100mm on the diaphragm, randomly select 5 test areas in the test sample, and read the particle size of each particle in each test area at a certain magnification (for example, 500 times or more); count the number of particles and particle size values ​​in each test area, and take the arithmetic mean of the particle size of all particles in each test area as the average particle size of the particles. In order to ensure the accuracy of the test results, 10 test samples can be taken for the above test, and the average value of each test sample is taken as the final test result. The testing instrument is ZEISS Sigma 300. It should be noted that when the particles are irregular in shape, the distance between the two farthest points on the particle is taken as the particle size of the particle.

[0207] The diameter of the cavity of the second microsphere particle refers to the straight-line distance passing through the center of the hollow cavity and extending to both ends of the hollow cavity, which can be measured by taking an average value of 50 positions in the diaphragm cross-section image.

[0208] The thickness of the shell of the second microsphere particle refers to the distance between the inner surface and the outer surface of the second microsphere particle. The distance between the inner surface and the outer surface of the second microsphere particle can be measured at 50 positions in the diaphragm cross-section image and then the average value is taken.

[0209] (2) Ionic impedance test of porous coating of diaphragm

[0210] The test sample (such as a porous substrate or a separator) is combined with two electrode plates to form a symmetrical battery. The number of layers of the test sample in the symmetrical battery is superimposed in a gradient design, and the number of test sample layers is set as follows: 2, 4, 6, 8, 10, and 12. The two electrode plates of the symmetrical battery are negative electrode plates that have not undergone charge and discharge cycles (i.e., fresh negative electrode plates prepared according to the method of Example 1).

[0211] The impedance values ​​of the symmetrical cells with different test sample numbers were measured using an electrochemical workstation (EIS). Gradient data fitting was then performed on the measured ionic impedance values ​​of the symmetrical cells with different test sample numbers. The ionic impedance of the single-layer test sample was calculated based on the fitting results (in Ω). The test temperature was 25°C.

[0212] The ionic resistance of the porous coating = the ionic resistance of the separator - the ionic resistance of the porous substrate.

[0213] (3) Air permeability test of porous substrates and diaphragms

[0214] At a temperature of 25°C and a humidity of less than 80%, a test sample (such as a porous substrate or membrane) is prepared into a 4cm×4cm area. The air permeability is measured using an Air-permeability-tester using the Gurley test (100mL) mode. The air permeability value (in seconds) is the time required for 100mL of air to pass through the 4cm×4cm test sample.

[0215] (4) Thermal shrinkage test of diaphragm

[0216] Cut the diaphragm into samples with a length of 70 mm in the MD direction and 50 mm in the TD direction, fix the four corners of the sample on a piece of paper with tape, and then bake the above sample in a 130°C oven for 1 hour. After the baking, take out the sample and measure the length L1 of the diaphragm in the MD direction and the length L2 in the TD direction.

[0217] The thermal shrinkage rate of the separator in the MD direction = (70-L1) / 70×100%.

[0218] The thermal shrinkage rate of the separator in the TD direction = (50-L2) / 50×100%.

[0219] To ensure the accuracy of the above test results, 5 samples were taken for testing in each embodiment and comparative example, and the average value was taken as the test result.

[0220] (5) Cycle performance test of lithium-ion secondary batteries

[0221] Allow the lithium-ion secondary battery to rest at 25°C for 60 minutes. Then charge it at a constant current rate of 0.5C to a full charge voltage of 4.25V. Continue charging at a constant voltage of 4.25V to a cutoff current of 0.02C. After resting for 5 minutes, discharge it at a constant current rate of 0.5C to 3.0V. This constitutes one charge-discharge cycle, and the discharge capacity at the first cycle is recorded. Repeat these steps for 1000 cycles of the lithium-ion secondary battery, and the discharge capacity after 1000 cycles is recorded.

[0222] Capacity retention rate of a lithium-ion secondary battery after 1000 cycles = (discharge capacity after 1000 cycles / discharge capacity at the first cycle) × 100%.

[0223] Example 1

[0224] (1) Preparation of diaphragm

[0225] The first filler particles, the second microsphere filler, and the polyacrylic acid binder were thoroughly dispersed in deionized water at a solid-to-weight ratio of 91:5:4 to form a porous coating slurry. The porous coating slurry was evenly coated on both surfaces of a 5-μm-thick polyethylene porous substrate and then oven-dried to form a separator. The porous coating had a thickness of 2 μm, and the separator had a thickness of 9 μm.

[0226] The first filler particles are boehmite, and the average particle size is 1 μm.

[0227] The second microsphere particle includes a cavity and a shell encapsulating the cavity. The shell includes a plurality of pores and comprises a first shell layer and a second shell layer. The second shell layer is located between the first shell layer and the cavity of the second microsphere particle. The first shell layer is polystyrene, and the second shell layer is a copolymer of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate. The mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5. The first shell layer and the second shell layer are connected by a C-C covalent bond. The diameter of the cavity is 0.6 μm, the average thickness of the shell is 0.1 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.75:1.

[0228] (2) Preparation of negative electrode sheet

[0229] Artificial graphite, acetylene black, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed at a solids-to-weight ratio of 96:1:1.5:1.5. Deionized water was then added as a solvent to create a slurry with a solids content of 70%, which was then stirred thoroughly. The slurry was evenly coated on one surface of an 8μm-thick copper foil. After drying at 110°C and cold pressing, a single-sided negative electrode sheet with a 150μm-thick negative electrode active material layer was obtained. The above steps were repeated on the other surface of the copper foil to obtain a double-sided negative electrode sheet. The negative electrode sheet was cut into 80mm x 880mm dimensions and the tabs were welded before use.

[0230] (3) Preparation of positive electrode sheet

[0231] LiCoO2, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in a solid-to-metal ratio of 94:3:3. N-methylpyrrolidone (NMP) was then added as a solvent to form a slurry with a solid content of 75%, which was then stirred evenly. The slurry was evenly coated on one surface of a 12μm thick aluminum foil. After drying at 90°C and cold pressing, a single-sided positive electrode sheet with a 100μm thick positive electrode active material layer was obtained. The above steps were then repeated on the other surface of the aluminum foil to obtain a double-sided positive electrode sheet. The positive electrode sheet was cut into a size of 74mm×867mm and the tabs were welded before use.

[0232] (4) Preparation of electrolyte

[0233] In an environment with a water content of less than 10 ppm, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC) were mixed in a mass ratio of 20:30:20:28:2, and then LiPF6 was added and mixed uniformly to obtain an electrolyte. The mass fraction of LiPF6 in the electrolyte was 8%.

[0234] (5) Preparation of lithium-ion secondary batteries

[0235] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked and wound in order to obtain an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dehydrated at 80°C, injected with the prepared electrolyte, and subjected to vacuum packaging, static standing, hot pressing, and shaping to obtain a soft-pack lithium-ion secondary battery.

[0236] Example 2

[0237] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0238] The second microsphere particle includes a cavity and a shell encapsulating the cavity. The shell includes a plurality of pores. The shell includes a first shell layer and a second shell layer. The second shell layer is located between the first shell layer and the cavity of the second microsphere particle. The first shell layer is polystyrene, and the second shell layer is a copolymer of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate. The mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5. The first shell layer and the second shell layer are connected by a C-C covalent bond. The diameter of the cavity is 0.7 μm, the average thickness of the shell is 0.05 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.88:1.

[0239] Example 3

[0240] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0241] The second microsphere particle includes a cavity and a shell encapsulating the cavity. The shell includes a plurality of pores. The shell includes a first shell layer and a second shell layer. The second shell layer is located between the first shell layer and the cavity of the second microsphere particle. The first shell layer is polystyrene, and the second shell layer is a copolymer of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate. The mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5. The first shell layer and the second shell layer are connected by a C-C covalent bond. The diameter of the cavity is 0.64 μm, the average thickness of the shell is 0.08 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.8:1.

[0242] Example 4

[0243] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0244] The second microsphere particle includes a cavity and a shell encapsulating the cavity. The shell includes a plurality of pores and comprises a first shell layer and a second shell layer. The second shell layer is located between the first shell layer and the cavity of the second microsphere particle. The first shell layer is polystyrene, and the second shell layer is a copolymer of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate. The mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5. The first shell layer and the second shell layer are connected by a C-C covalent bond. The diameter of the cavity is 0.5 μm, the average thickness of the shell is 0.15 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.63:1.

[0245] Example 5

[0246] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0247] The second microsphere particle includes a cavity and a shell encapsulating the cavity. The shell includes a plurality of pores and comprises a first shell layer and a second shell layer. The second shell layer is located between the first shell layer and the cavity of the second microsphere particle. The first shell layer is polystyrene, and the second shell layer is a copolymer of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate. The mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5. The first shell layer and the second shell layer are connected by a C-C covalent bond. The diameter of the cavity is 0.4 μm, the average thickness of the shell is 0.2 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.5:1.

[0248] Example 6

[0249] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0250] The second microsphere particle includes a cavity and a shell encapsulating the cavity. The shell includes a plurality of pores and comprises a first shell layer and a second shell layer. The second shell layer is located between the first shell layer and the cavity of the second microsphere particle. The first shell layer is polystyrene, and the second shell layer is a copolymer of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate. The mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5. The first shell layer and the second shell layer are connected by a C-C covalent bond. The diameter of the cavity is 0.8 μm, the average thickness of the shell is 0.1 μm, the average particle size of the second microsphere particle is 1 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.8:1.

[0251] Example 7

[0252] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0253] The second microsphere particle includes a cavity and a shell encapsulating the cavity. The shell includes a plurality of pores and comprises a first shell layer and a second shell layer. The second shell layer is located between the first shell layer and the cavity of the second microsphere particle. The first shell layer is polystyrene, and the second shell layer is a copolymer of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate. The mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5. The first shell layer and the second shell layer are connected by a C-C covalent bond. The diameter of the cavity is 0.4 μm, the average thickness of the shell is 0.1 μm, the average particle size of the second microsphere particle is 0.6 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.67:1.

[0254] Example 8

[0255] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0256] The second microsphere particle includes a cavity and a shell encapsulating the cavity. The shell includes a plurality of pores and comprises a first shell layer and a second shell layer. The second shell layer is located between the first shell layer and the cavity of the second microsphere particle. The first shell layer is polystyrene, and the second shell layer is a copolymer of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate. The mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5. The first shell layer and the second shell layer are connected by a C-C covalent bond. The diameter of the cavity is 0.9 μm, the average thickness of the shell is 0.05 μm, the average particle size of the second microsphere particle is 1 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.9:1.

[0257] Example 9

[0258] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0259] The second microsphere particle includes a cavity and a shell encapsulating the cavity. The shell includes a plurality of pores. The shell includes a first shell layer and a second shell layer. The second shell layer is located between the first shell layer and the cavity of the second microsphere particle. The first shell layer is polystyrene, and the second shell layer is a copolymer of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate. The mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5. The first shell layer and the second shell layer are connected by a C-C covalent bond. The diameter of the cavity is 0.1 μm, the average thickness of the shell is 0.05 μm, the average particle size of the second microsphere particle is 0.2 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.5:1.

[0260] Comparative Example 1

[0261] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0262] (1) Preparation of diaphragm

[0263] Deionized water and boehmite particles are pre-dispersed, and then a polyacrylic acid binder is added and continued to be stirred and mixed evenly. Then, a wetting agent, dimethylsiloxane, is added, stirred evenly, and degassed to obtain a porous coating slurry. The porous coating slurry is evenly coated on a polyethylene porous substrate with a thickness of 5 μm, and then dried in an oven to obtain a diaphragm.

[0264] The average boehmite particle size is 1 μm. The solid mass ratio of boehmite particles, binder, and wetting agent is 95:4:1. The thickness of the porous coating is 2 μm, and the thickness of the separator is 9 μm.

[0265] Comparative Example 2

[0266] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0267] The second microsphere particle includes a cavity and a shell encapsulating the cavity. The shell includes a plurality of pores and comprises a first shell layer and a second shell layer. The second shell layer is located between the first shell layer and the cavity of the second microsphere particle. The first shell layer is polystyrene, and the second shell layer is a copolymer of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate. The mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5. The first shell layer and the second shell layer are connected by a C-C covalent bond. The diameter of the cavity is 0.76 μm, the average thickness of the shell is 0.02 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.95:1.

[0268] Comparative Example 3

[0269] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0270] The second microsphere particle includes a cavity and a shell encapsulating the cavity. The shell includes a plurality of pores and comprises a first shell layer and a second shell layer. The second shell layer is located between the first shell layer and the cavity of the second microsphere particle. The first shell layer is polystyrene, and the second shell layer is a copolymer of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate. The mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5. The first shell layer and the second shell layer are connected by a C-C covalent bond. The diameter of the cavity is 0.2 μm, the average thickness of the shell is 0.3 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.25:1.

[0271] Comparative Example 4

[0272] The preparation process of the lithium ion secondary battery is the same as that of Example 1, except that the porous coating layer of the separator does not contain the first filler particles.

[0273] Table 1

[0274]

[0275] It can be seen from the above test results that the porous coating of the diaphragm in this application includes first filler particles and second microsphere particles, and the average thickness of the shell of the second microsphere particles is 0.05μm to 0.2μm. The diaphragm has high heat resistance, good electrolyte wettability and good electrolyte retention. The lithium-ion secondary battery using the diaphragm has good cycle performance.

[0276] The porous coating layer of the separator of Comparative Example 1 does not include the second microsphere particles, the separator has poor electrolyte wettability and electrolyte retention, and the cycle performance of the lithium ion secondary battery is poor.

[0277] The porous coating of the diaphragm of Comparative Example 2 includes first filler particles and second microsphere particles, but the average thickness of the shell of the second microsphere particles is less than 0.05 μm, and the heat resistance of the diaphragm is poor. At the same time, during the long-term cycle charge and discharge process of the lithium-ion secondary battery, the second microsphere particles are easily broken, resulting in poor long-cycle performance of the lithium-ion secondary battery.

[0278] The porous coating of the diaphragm of Comparative Example 3 includes first filler particles and second microsphere particles, but the average thickness of the shell of the second microsphere particles is greater than 0.2 μm, and the smaller the electrolyte storage space it can provide, the smaller the improvement effect on the liquid swelling problem and the interface purple spot lithium precipitation problem, which leads to poor cycle performance of the lithium-ion secondary battery.

[0279] The porous coating layer of the diaphragm of Comparative Example 4 does not include the first filler particles. When the porous coating layer does not contain the first filler particles boehmite, the heat resistance of the diaphragm will deteriorate, and the thermal safety performance of the lithium-ion secondary battery will deteriorate. At the same time, the mechanical strength of the diaphragm will also be reduced, and it will be easy to deform during the cyclic charge and discharge process of the lithium-ion secondary battery, thereby causing the cycle performance of the lithium-ion secondary battery to deteriorate.

[0280] Example 1-1

[0281] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0282] The solid content mass ratio of the first filler particles, the second microsphere filler, and the polyacrylic acid binder is 73:20:7.

[0283] Example 1-2

[0284] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0285] The solid content mass ratio of the first filler particles, the second microsphere filler, and the polyacrylic acid binder is 80:16:4.

[0286] Examples 1-3

[0287] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0288] The solid content mass ratio of the first filler particles, the second microsphere filler, and the polyacrylic acid binder is 85:11:4.

[0289] Examples 1-4

[0290] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0291] The solid content mass ratio of the first filler particles, the second microsphere filler, and the polyacrylic acid binder is 94:2:4.

[0292] Table 2

[0293]

[0294] From the above test results, it can be seen that further adjusting the content of the first filler particles, the second microsphere particles and the binder is beneficial for the separator to better combine high heat resistance, good electrolyte wettability and good electrolyte retention, which is beneficial to improving the cycle performance of lithium-ion secondary batteries.

[0295] Example 2-1

[0296] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0297] The first filler particles are boehmite, and the average particle size is 0.1 μm.

[0298] Example 2-2

[0299] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0300] The first filler particles are boehmite, and the average particle size is 2 μm.

[0301] Example 2-3

[0302] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0303] The first filler particles are boehmite, and the average particle size is 2.2 μm.

[0304] Table 3

[0305]

[0306] From the above test results, it can be seen that further adjusting the average particle size of the first filler particles is beneficial for the separator to better combine high heat resistance, high air permeability and low ionic impedance, which is beneficial to improving the cycle performance of lithium-ion secondary batteries.

[0307] Example 3-1

[0308] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0309] The second microsphere particle includes a cavity and a shell encapsulating the cavity. The shell includes a plurality of pores and comprises a first shell layer and a second shell layer. The second shell layer is located between the first shell layer and the cavity of the second microsphere particle. The first shell layer is polystyrene, and the second shell layer is a copolymer of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate. The mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 20:80:10. The first shell layer and the second shell layer are connected by a C-C covalent bond. The diameter of the cavity is 0.6 μm, the average thickness of the shell is 0.1 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.75:1.

[0310] Example 3-2

[0311] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0312] The second microsphere particle includes a cavity and a shell encapsulating the cavity. The shell includes a plurality of pores and comprises a first shell layer and a second shell layer. The second shell layer is located between the first shell layer and the cavity of the second microsphere particle. The first shell layer is polystyrene, and the second shell layer is a copolymer of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate. The mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 30:70:1. The first shell layer and the second shell layer are connected by a C-C covalent bond. The diameter of the cavity is 0.6 μm, the average thickness of the shell is 0.1 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.75:1.

[0313] Example 3-3

[0314] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0315] The second microsphere particle includes a cavity and a shell encapsulating the cavity. The shell includes a plurality of pores. The shell includes a first shell layer and a second shell layer. The second shell layer is located between the first shell layer and the cavity of the second microsphere particle. The first shell layer is polystyrene, and the second shell layer is a copolymer of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate. The mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 15:85:11. The first shell layer and the second shell layer are connected by a C-C covalent bond. The diameter of the cavity is 0.6 μm, the average thickness of the shell is 0.1 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.75:1.

[0316] Examples 3-4

[0317] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0318] The second microsphere particle includes a cavity and a shell encapsulating the cavity. The shell includes a plurality of pores and comprises a first shell layer and a second shell layer. The second shell layer is located between the first shell layer and the cavity of the second microsphere particle. The first shell layer is polystyrene, and the second shell layer is a copolymer of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate. The mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 45:5:0.2. The first shell layer and the second shell layer are connected by a C-C covalent bond. The diameter of the cavity is 0.6 μm, the average thickness of the shell is 0.1 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.75:1.

[0319] Table 4

[0320]

[0321] From the above test results, it can be seen that further adjusting the ratio of soft monomer structural units, hard monomer structural units, and cross-linked structural units in the second shell layer of the second microsphere particles is beneficial for the separator to better combine high permeability and low ionic impedance, which is beneficial to improving the cycle performance of lithium-ion secondary batteries.

[0322] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present application, and such modifications or substitutions should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A separator comprising a porous substrate and a porous coating disposed on at least one side of the porous substrate, characterized in that: The porous coating layer includes first filler particles, second microsphere particles and a binder. The first filler particles are solid structures. The second microsphere particles include a cavity and a shell covering the cavity. The average thickness of the shell is 0.05 μm to 0.2 μm.

2. The diaphragm according to claim 1, characterized in that The average thickness of the shell is 0.05 μm to 0.1 μm.

3. The diaphragm according to claim 1, characterized in that The porous coating layer satisfies at least one of the following conditions (1) to (6): (1) The average particle size of the first filler particles is 0.2 μm to 2 μm; (2) the average particle size of the second microsphere particles is 0.2 μm to 1 μm; (3) The diameter of the cavity of the second microsphere particle is 0.1 μm to 0.9 μm; (4) a ratio of the diameter of the cavity of the second microsphere particle to the average particle diameter of the second microsphere particle is 0.6:1 to 0.9:1; (5) The specific surface area of ​​the second microsphere particles is 5m 2 / g to 30m 2 / g; (6) The shell includes a plurality of pore structures, and the average pore diameter of the pore structures of the shell is less than 20 nm.

4. The diaphragm according to claim 3, characterized in that The porous coating layer satisfies at least one of the following conditions (1) to (4): (1) The average particle size of the first filler particles is 0.6 μm to 1 μm; (2) the average particle size of the second microsphere particles is 0.6 μm to 1 μm; (3) The diameter of the cavity of the second microsphere particle is 0.4 μm to 0.8 μm; (4) The ratio of the diameter of the cavity of the second microsphere particles to the average particle size of the second microsphere particles is 0.6:1 to 0.88:

1.

5. The diaphragm according to claim 1, characterized in that The average particle size of the first filler particles is greater than or equal to the average particle size of the second microsphere particles.

6. The diaphragm according to claim 1, characterized in that The mass proportion of the first filler particles in the porous coating layer is 73% to 94%. The mass proportion of the second microsphere particles in the porous coating layer is 2% to 20%. The binder accounts for 1% to 7% by mass in the porous coating layer.

7. The diaphragm according to claim 6, characterized in that The mass proportion of the first filler particles in the porous coating layer is 80% to 91%. The mass proportion of the second microsphere particles in the porous coating layer is 5% to 16%. The binder accounts for 1% to 5% by mass in the porous coating layer.

8. The diaphragm according to claim 1, characterized in that The diaphragm satisfies at least one of the following conditions (1) to (2): (1) The ionic resistance of the porous coating of the separator is 0.001Ω to 0.15Ω; (2) The difference between the air permeability of the diaphragm and the air permeability of the porous substrate is greater than 0 and less than or equal to 20 s / 100 ml.

9. The diaphragm according to claim 1, wherein After the second microsphere particles are immersed in an electrolyte at 60° C. for 24 hours, the thickness growth rate of the shell is less than or equal to 80%.

10. The diaphragm according to claim 1, wherein The shell of the second microsphere particle includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity of the second microsphere particle, the first shell layer includes polystyrene, the second shell layer includes an acrylic polymer, and the first shell layer and the second shell layer are connected by a CC covalent bond.

11. The diaphragm according to claim 10, characterized in that The acrylic polymer comprises a soft monomer structural unit and a hard monomer structural unit, The soft monomer structural unit includes at least one of n-butyl acrylate structural unit, n-pentyl acrylate structural unit, isopentyl acrylate structural unit, isooctyl acrylate structural unit, 2-ethylhexyl acrylate structural unit, 2-nonyl acrylate structural unit, isononyl acrylate structural unit, decyl acrylate structural unit, undecyl acrylate structural unit, lauryl acrylate structural unit, tridecyl acrylate structural unit, octadecyl acrylate structural unit, decyl methacrylate structural unit, undecyl methacrylate structural unit, lauryl methacrylate structural unit, tridecyl methacrylate structural unit, and octadecyl methacrylate structural unit. The hard monomer structural unit includes at least one of a methyl acrylate structural unit, a methyl methacrylate structural unit, a vinyl acetate structural unit, an acrylonitrile structural unit, an acrylamide structural unit, and a styrene structural unit.

12. The diaphragm according to claim 11, characterized in that The mass ratio of the soft monomer structural unit to the hard monomer structural unit is 40:60 to 20:

80.

13. The diaphragm according to claim 11, characterized in that The acrylic polymer also includes a multifunctional cross-linking structural unit, The multifunctional cross-linked structural unit includes at least one of an ethylene glycol dimethacrylate structural unit, a polyethylene glycol dimethacrylate structural unit, a butylene glycol dimethacrylate structural unit, a hexanediol dimethacrylate structural unit, a polybutadiene dimethacrylate structural unit, a polyurethane dimethacrylate structural unit, a propoxylated glycerol trimethacrylate structural unit, and a divinylbenzene structural unit; and / or, The mass of the multifunctional cross-linked structural unit is 0.1% to 10% of the total mass of the soft monomer structural unit and the hard monomer structural unit.

14. The diaphragm according to claim 13, characterized in that The acrylic polymer is composed of n-butyl acrylate structural units, methyl acrylate structural units, and ethylene glycol dimethacrylate structural units. In the acrylic polymer, the mass ratio of the n-butyl acrylate structural units to the methyl acrylate structural units is 40:60 to 20:80, and the mass of the ethylene glycol dimethacrylate structural units is 0.5% to 10% of the total mass of the n-butyl acrylate structural units and the methyl acrylate structural units.

15. The diaphragm according to claim 1, wherein The diaphragm satisfies at least one of the following conditions (1) to (3): (1) The specific surface area of ​​the first filler particles is less than or equal to 20 m 2 / g; (2) The glass transition temperature T of the binder g -40℃ to 15℃; (3) The adhesive includes at least one of polymethacrylate adhesive, styrene-butadiene rubber, polyacrylic acid, and polyacrylate.

16. The diaphragm according to claim 1, wherein The diaphragm satisfies at least one of the following conditions (1) to (6): (1) The thickness of the porous substrate is 2 μm to 7 μm; (2) The thickness of the porous coating layer is 0.5 μm to 3 μm; (3) The total thickness of the diaphragm is 2.5 μm to 10 μm; (4) The bonding force between the porous substrate and the porous coating is 30 N / m to 100 N / m; (5) The longitudinal thermal shrinkage of the diaphragm when heated at 130° C. for 1 hour is less than or equal to 5%; (6) The transverse heat shrinkage of the diaphragm when heated at 130° C. for 1 hour is less than or equal to 5%.

17. An electrochemical device, characterized in that The invention comprises a positive electrode sheet, a negative electrode sheet and a separator according to any one of claims 1 to 16, wherein the separator is located between the positive electrode sheet and the negative electrode sheet.

18. An electronic device, characterized in that: Comprising the electrochemical device according to claim 17.

19. A method for preparing the diaphragm according to any one of claims 1 to 16, characterized in that: The steps include: providing a porous substrate; Providing a porous coating slurry comprising first filler particles, second microsphere particles, and a binder, wherein the first filler particles are solid structures, the second microsphere particles comprise a cavity and a shell covering the cavity, and the average thickness of the shell is 0.05 μm to 0.2 μm; The porous coating slurry is coated on at least one side of the porous substrate and dried to obtain a separator.

Images